The present invention relates to a method and an apparatus for cutting a plate-shaped brittle material into two plate pieces. More particularly, the present invention relates to a method and an apparatus of the foregoing type preferably employable in case that a plurality of elements are formed on a plate-shaped brittle material having a small thickness to produce a semiconductor sensor, a solar cell, an integrated circuit tip, a liquid crystal display element or the like, and subsequently, the plate-shaped brittle material is cut into a plurality of element units each usable as a component. Further, the present invention relates to an apparatus for forming a cut groove in a plate-shaped brittle material in conformity with a predetermined cutting pattern using a rotary disc type scribing tip.
In general, a method of cutting a plate-shaped brittle material such as a glass plate or the like in conformity with a predetermined pattern is classified into two methods, one of them being such that a cut groove exhibiting the foregoing predetermined pattern is formed in a plate-shaped brittle material by actuating a tool made of diamond, cemented tungsten carbide or the like and the other one being such that a part of the plate-shaped brittle material such as a glass plate or the like is cut therefrom by operating a machine tool such as a laser working machine, a slicer or the like.
With the first-mentioned method classified in that way, a certain intensity of moment is usually applied to a plate-shaped brittle material with a cut groove as a datum point so as to impart a tensile force to the plate-shaped brittle material, and it has been known that a cut surface having excellent appearance can be formed for a short time with a small magnitude of imparted power by employing the first-mentioned method. Incidentally, the foregoing fact is applicable only to case that a plate-shaped brittle material is cut in conformity with a linear pattern. However, in case that the plate-shaped brittle material is to be cut in conformity with a cutting pattern including bent parts, it is practically difficult to uniformly apply moment to the cut groove formed in the plate-shaped brittle material Thus, in this case, there arises a problem that a cut edge slantwise extends, causing an unacceptable cut surface to be undesirably formed without any possibility that the plate-shaped brittle material can correctly be cut in conformity with a predetermined cut groove.
To solve the foregoing problem, a proposal has been made with respect to a cutting method for which friction is utilized (see NO. 513, Vol. 55, A collection of treatises edited by The Japan Mechanical Engineering Association (Edition C), published on May, 1989). According to this proposal, the cutting method is practiced in such a manner that the plate-shaped brittle material having a cut groove formed therein is clamped between a pair of pressing plates each having an elastic modulus smaller than that of the plate-shaped brittle material, and subsequently, an assemble of the plate-shaped brittle material and the pressing plates is compressed in the vertical direction by operating a press machine until the pressing plates are broken, causing the power effective in the outward orienting direction to be applied to the cut groove, whereby the plate-shaped brittle material can be cut in conformity with a predetermined pattern.
The foregoing proposed cutting method makes it possible to correctly cut a plate-shaped brittle material in conformity with any other pattern rather than a linear line, because no moment is applied to the plate-shaped brittle material. However, to assure that a high intensity of power enough to properly achieve each cutting operation is imparted to the cut groove formed in the plate-shaped brittle material by utilizing the power effective in the outward orienting direction applied to the pressing plates, a large magnitude of pressing power is required, resulting in the press machine being unavoidably designed and constructed with large dimensions.
In case that an item to be cut is a semiconductor sensor, a solar cell, an integrated circuit tip, a liquid crystal display element or the like, since there often arises an occasion that a complicated and fine circuit pattern, a deposited film or the like is formed on a plate-shaped brittle material, there is a high risk that the circuit pattern, the deposited film or the like are damaged or injured by the pressing power given by the press machine.
In addition, another method similar to the first-mentioned one wherein a laser light beam is irradiated to a cut groove formed in a plate-shaped brittle material in conformity with a predetermined pattern so that cracks formed in association with the cut groove progressively grow by the thermal stress induced by the irradiation of the laser light beam, causing the plate-shaped brittle material to be cut in conformity with the foregoing predetermined pattern is disclosed in an official gazette of Japanese Patent Laid-Open Publication NO. 62-46930.
With this method disclosed in that way, since no moment is applied to the plate-shaped brittle material, and moreover, no energy is given to the cut groove, the problem inherent to the first-mentioned method does not appear on the plate-shaped brittle material. However, since the thermal stress is utilized for the purpose of cutting the plate-shaped brittle material into plate pieces, there arises an occasion that the pattern of the cut groove is adversely affected by the heat generated by the irradiation of the laser light beam, and the cracks do not grow further in the predetermined direction due to the stress remaining in the plate-shaped brittle material and the presence of another fine cracks rather than the cut groove. Further, since the laser working machine is very expensive and the plate-shaped brittle material is practically cut at a low working speed, there arises a drawback that a cost required for achieving each cutting operation is undesirably raised up.
In addition, a method of cutting a plate-shaped brittle material into plate pieces by utilizing heat generated by irradiation of a laser light beam, a method of cutting the same by injecting a high pressure water stream to the plate-shaped brittle material and a method of cutting the same by recirculatively driving a wire saw can be noted as another methods modified from the last-mentioned method classified in the aforementioned manner. However, each of the foregoing methods has a drawback that each cutting operation is achieved at a low efficiency due to a slow working speed thereof.
Further, to form or scribe a cut groove in a plate-shaped brittle material, a method of using a scribing tip made of diamond, hard metal (cemented carbide) or the like for cutting the plate-shaped brittle material has been usually employed for satisfactorily accomplishing the foregoing purpose. In case that the cut groove is formed in the shape of a curved line, an imbalance stress is applied to the plate-shaped brittle plate during each scribing operation, causing the scribing crack formed in association with the cut groove to be bent at a substantially right angle relative to the direction of a depth of the cut groove (see FIG. 10(a)). When the plate-shaped brittle plate is cut into two plate pieces while the foregoing state is maintained, the cut edge is slantwise warped. Thus, there a rises a problem that the cut surface exhibits unacceptable appearance because so-called burrs are formed along the cut edge (see FIG. 10(b)).